The present invention relates to a plant and process for removing carbon dioxide from industrial gas streams and effluents with a view to reducing carbon dioxide emissions to the environment.
The concentration of carbon dioxide in the atmosphere has risen from 280 parts per million to 370 parts per million over the last 150 years mainly from increased use of fossil fuels, particularly for electrical power generation and transport. However, a rapid move to meet all energy needs through alternative renewable energy sources would be very costly to consumers, damaging to the economy, and at the present time is impractical on a technology basis.
A reduction in carbon dioxide emissions will be required to stabilize, and in the long term, decrease carbon dioxide concentrations in the atmosphere. A promising technology for significantly decreasing emissions from large scale carbon dioxide emitting plants such as coal fired power stations, cement plants, gas processing facilities and iron smelting plants involve separating and capturing the carbon dioxide from the process streams, compressing the carbon dioxide and then storing the carbon dioxide in a manner that will prevent the carbon dioxide from leaking to the atmosphere.
Capturing carbon dioxide from gas streams to produce gas streams rich in carbon dioxide has been practiced in food and chemical industries for some time. For example, natural gas producers have routinely separated carbon dioxide from hydrocarbon gases which are then transported to consumers via pipeline.
In brief, technology currently used for separating carbon dioxide from gas streams include:                physical solvents such as methanol and chemical solvents such as monoethanolamine (MEA) for absorbing carbon dioxide;        various types of membranes for separating carbon dioxide from gases;        absorbing carbon dioxide onto zeolites and other solids; and        low temperature separation.        
These methods can be applied to a range of industrial gas streams. However, the methods currently available are not particularly efficient for removing carbon dioxide from high volume low pressure industrial gas streams having a low concentration of carbon dioxide such as the flue gases generated by conventional coal fired and gas fired power stations. In particular, the massive volumes of flue gases generated by power stations require large capital investments to handle the flue gas which is seen as a major impediment. Another difficulty is that a large amount of energy, approximately 30-40% of the total production of a coal powered electrical generation plant would be required to release the carbon dioxide from solvents or solid absorbing mediums after separation from the flue gas. In addition, technologies such as membrane separation are yet to be adequately scaled up to the level where they can be used to capture carbon dioxide at the scale of coal fired power stations.
It is therefore an object of the present invention to provide an alternative process and plant for removing carbon dioxide from industrial gas streams.